<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>造型函数</title>
</head>
<body>
  <script src="../common/lib/gl-renderer.js"></script>
  <canvas width="512" height="512"></canvas>
  <script>
    const vertex = `
      attribute vec2 a_vertexPosition;
      attribute vec2 uv;

      varying vec2 vUv;

      void main() {
        gl_PointSize = 1.0;
        vUv = uv;
        gl_Position = vec4(a_vertexPosition, 1, 1);
      }
    `;

    const fragment = `
      #ifdef GL_ES
      precision highp float;
      #endif

      varying vec2 vUv;

      void main() {
        // gl_FragColor = vec4(0, 0, 0, 1);

        // vec2 st = vUv * 10.0;
        // gl_FragColor.rgb = vec3(fract(st), 0.0);
        // gl_FragColor.a = 1.0;

        vec2 st = vUv * 10.0;
        vec2 idx = floor(st);
        vec2 grid = fract(st);
  
        vec2 t = mod(idx, 2.0);
        
        if(t.x == 1.0) {
          grid.x = 1.0 - grid.x;
        }
        if(t.y == 1.0) {
          grid.y = 1.0 - grid.y;
        }
        gl_FragColor.rgb = vec3(grid, 0.0);
        gl_FragColor.a = 1.0;
      }
    `;

    const canvas = document.querySelector('canvas');
    const renderer = new GlRenderer(canvas);
    const program = renderer.compileSync(fragment, vertex);
    renderer.useProgram(program);

    renderer.setMeshData([{
      positions: [
        [-1, -1],
        [-1, 1],
        [1, 1],
        [1, -1],
      ],
      attributes: {
        uv: [
          [0, 0],
          [0, 1],
          [1, 1],
          [1, 0],
        ],
      },
      cells: [[0, 1, 2], [2, 0, 3]],
    }]);

    renderer.render();
  </script>
</body>
</html>